Update
on 2009-11-12 08:04 by Stu
If you do set up your 5D as described above, make sure to do the last step with the custom function so that these settings only affect your video shooting. You probably don’t want to have Highlight Tone Priority on for your stills, especially if you shoot raw. What it does is “push” (reduce) your ISO setting by one stop, causing you to capture a full stop of additional highlight information through no more sophisticated means than simply underexposing. For video and JPEGs, that additional highlight range is non-linearly mapped into the image, creating a very film-like “shoulder.” For raw, it simply passes metadata to your raw decoder that may or may not be honored.
Lightroom, for example, interprets HTP as a simple instruction to boost exposure by one stop. Fair enough, except that this won’t match what you saw on the camera LCD at all. Blacks will be too crushed and that extra highlight detail will be missing (until you futz with the Develop controls to bring it back). Trying to bring more detail back into the blacks will bring in nasty noise that was not visible in the JPEG preview.
Underexposing to capture extra highlight info can be a fine idea, but it’s best implemented case-by-case, and in a predictable way.
Highlight Tone Priority hides the underexposure from you and might cause you to think you’re capturing a more robust negative than you really are.
But for video mode, it creates a more film-like low-contrast, high dynamic range image, with just a touch more noise from the one-stop push.
I now roll with two custom function settings, one with HTP on, one with it off. For daylight exteriors with plenty of light, HTP: On. For lower-light situations, or more controlled lighting, HTP: Off.
Update
on 2009-08-24 21:13 by Stu
There’s an interesting discussion of the nuances of HTP and ISO performance over at cinema5D.com. Interpret tests results such as these with caution though — as the OP says, he’s trying to show off the noise, so it’s not so much a real-world test as it is an attempt to learn more about what’s happening in the camera. Turns out there are some surprizing variations in noise preformance at different ISO settings, possibly having to do with some ISO settings being “virtual,” i.e. metadata offsets of native settings.